Three-level AC-DC Power Electronic Transformer DC Bus Capacitor Pre-charging Method

Abstract

The invention discloses a pre-charging method for a three-level alternating current / direct current power electronic transformer direct current bus capacitor. In a charging process, firstly, connection between equipment and an alternating current / direct current power distribution network is cut off; in different control periods, high-voltage side each-phase convertors take turns to select to input a corresponding quantity of PM (Power Modules), and high-frequency square wave voltage of 50% duty cycle is simultaneously output; in addition, low-voltage direct current side each-phase convertorsSM output square wave voltage of the same frequency and the same phase; and then, on a low-voltage side, auxiliary charging equipment is controlled, and through a resonant network formed by a capacitor CLFB and transformer leakage inductance Lr, a high voltage side direct current bus capacitor and a low voltage side direct current bus capacitor are charged. By use of the method, the current impactof the system in a charging process can be effectively lowered, meanwhile, the voltage of the high voltage side direct current bus capacitor and the voltage of the low voltage side direct current buscapacitor can be improved to a rated working condition operation value, and therefore, the alternating current side current impact of the equipment during synchronization can be reduced.

Description

technical field [0001] The invention relates to a method for precharging the capacitor of a DC bus bar of an AC and DC power electronic transformer. Background technique [0002] The future smart grid requires intelligent electrical equipment and superior electrical performance, such as high power supply quality and easy access to renewable energy power generation. The distribution network is an important part of the power grid. In the distribution network, distribution transformers are the most commonly used equipment. The annual output of distribution transformers in my country accounts for about 1 / 3 of the annual output of all transformers. Therefore, the performance of the distribution transformer is related to the performance of the future smart grid, and the traditional transformer is far from meeting the high power supply quality and intelligent requirements of the future smart grid. [0003] Power electronic transformers are also called solid-state transformers or e...

AI Technical Summary

Problems solved by technology

[0005] Before the power electronic transformer can operate normally, it is first necessary to charge the DC bus capacitors on the high and low voltage sides. The existing charging method can use the high-voltage AC power grid to charge the DC bus capacitors, such as patents CN 108696165A and CN103973094B. The operation and implementation are more convenient, and The technology is relatively mature, but the bus capacitor voltage cannot be charged to the rated value, and a high-voltage level charging resistor and circuit breaker are required. In addition, the charging resistor and circuit breaker are bulky and expensive, and the pre-charging operation from the high-voltage side also increases the charging time. hazards in the process

For three-stage AC-DC power electronic transformers, the method of using high-voltage AC grid charging still has problems such as the bus capacitor voltage cannot be charged to the rated value, the charging equipment is bulky, expensive, and dangerous.

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